The exemplary embodiment relates to sheet transport systems. It finds particular application in a printing system in which output streams of print media traveling in different directions from two or more marking engines are merged into a combined stream.
Electronic printing systems, such as laser printers and copiers, typically employ an input terminal which receives images in digital form and conversion electronics for converting the image to image signals or pixels. The printing system may include a scanner for scanning image-bearing documents or be connected to a computer network which supplies the digital images. The signals are stored and are read out successively to a marking engine for formation of the images and transfer of the images to a print medium, such as paper.
Cluster printing systems enable high print speeds or print rates by grouping a number of slower speed marking engines in parallel. These systems also enable output to be maintained, albeit at a slower speed, if one marking engine fails, through redirection of a print job to the remaining marking engines. Parallel printing systems have been developed which employ multiple marking engines for black, process (or full) color, and custom color (single color or monochrome) printing of selected pages within a print job. For example one marking engine prints even pages of a print job on one set of sheets while another marking engine prints the odd pages on a second set of sheets. The outputs of the marking engines are automatically combined in page order and delivered to a common finisher, such as an output tray.
Merging sheets from two paths into a single path has been achieved by aligning one stream with the other and merging the streams. However, the pathways needed for conveying one stream from a first marking engine over a second marking engine, which generates the second stream, and then bringing the two streams into alignment, tend to be lengthy. Additionally, in large, high speed printing systems, it has been found difficult to provide a bypass path over or under one of the marking engines.